1. Field of the Invention
The present invention relates to a battery pack, and more particularly, to a battery pack comprising a plurality of secondary batteries or a plurality of battery assemblies, each battery assembly including a plurality of unit batteries, and at least one safety switch, which is capable of providing a precise measurement of the voltages of the plurality of secondary batteries or battery assemblies.
2. Description of the Related Art
Recently, as compact and lightweight portable electronic or electrical appliances such as cellular phones, notebook computers and camcorders are actively developed and produced, these portable electronic or electrical appliances are typically accompanied by a battery pack intended to provide electrical power to the appliance in any place even without a separate power supply. Generally, a battery pack uses a chargeable and dischargeable secondary battery, which may be one of a nickel-cadmium (Ni—Cd) battery, a nickel-hydrogen (Ni-MH) battery or a lithium (Li) battery, in consideration of economical aspects.
The Li secondary battery is widely applied to the portable appliances because Li secondary battery has an operating voltage which is three times higher than other batteries (Ni—Cd and Ni-MH batteries), and a high energy density per unit weight. The Li secondary battery is classified into a Li ion battery using an aqueous electrolyte and a Li polymer battery using a polymer electrolyte formed on the electrolyte. The Li secondary battery may also be classified into cylindrical, prismatic and pouch batteries based on the shape.
Since a single secondary battery cannot provide a sufficient voltage or capacity to portable electronic or electrical appliances that are intended to operate for a long period of time, a plurality of secondary batteries or a plurality of battery assemblies, each battery assembly including a plurality of unit batteries, are electrically connected in series or parallel to constitute a battery pack.
Such a battery pack that is constructed with the plurality of secondary batteries or the plurality of battery assemblies, each battery assembly including the unit batteries, is repeatedly charged and discharged for several times, and each of the secondary batteries or unit batteries is charged with a different energy level. That is, since the plurality of secondary batteries or unit batteries are discharged to different energy levels, when recharged, the secondary battery or unit battery having relatively higher energy may be completely charged within a shorter time than that having relatively lower energy. Similarly, a battery having relatively lower energy starts to be discharged even when the battery has been incompletely charged. Therefore, the battery having relatively lower energy may be undesirably over discharged and become damaged due to repetitive incomplete charging and over-discharging.
To solve these problems, a battery pack that is constructed with a plurality of secondary batteries or a plurality of battery assemblies is typically constructed with a battery management system (BMS) which measures the voltage of each of the secondary batteries or battery assemblies to control charging and discharging operations of the secondary batteries or battery assemblies.
Generally, a contemporary battery pack may be constructed with a plurality of secondary batteries or a plurality of battery assemblies, each battery assembly including a plurality of unit batteries, a plurality of sensing lines, and a battery management system electrically connected with the sensing lines to measure the voltages of the plurality of secondary batteries or battery assemblies, and to control charging and discharging operations of the plurality of secondary batteries or battery assemblies.
Each of the plurality of sensing lines is electrically connected to a node located between two adjacent secondary batteries or battery assemblies. Therefore, the minimum quantity of the sensing lines for measuring the voltages of the secondary batteries or battery assemblies equals to the number of secondary batteries or battery assemblies plus one.
The contemporary battery pack may also be constructed with a safety switch which is electrically connected between the plurality of secondary batteries or battery assemblies in order to block an electrically current flowing through the plurality of secondary batteries or battery assemblies due to a breakdown of the battery pack. This battery pack has a problem, however, that the exact voltages of the secondary batteries or battery assemblies that are directly connected to the safety switch may not be precisely measured.